Expansible rotary drill bits



March 2, N6 A. w. KAMMERER ExRANsIRLE ROTARY DRILL BITS File'd July 26,1962 l am.

w w Q w www ad. 122m 1 INVENTOR. QCf/E@ M MMM/weee@ www@ 3,171,502EXPANSIBLE RTARY BREIL Bild Archer W. Kammerer, Fullerton, Calif.,assigner ont onefifth each to .lean K. Lamphere, Fullerton, Carr., andArcher W. Kammerer, Jr., Houston, Tex.

Filed .luly 26, i962, Ser, Noi. 2lZ,69l 7 Claims. (Cl. M5L-267) Thepresent invention relates to rotary drill bits, and more particularly tobits having expandible cutters'for enlarging the diameters of wellbores, milling out portions of casing strings in well bores, and thelike.

Rotary expansiblc drill bits have been used having cutters expandedoutwardly by the hydraulic pressure of fluid pumped down through tubulardrilling strings to which the bits are secured. When the drill bit is ofsmall size, the hydraulic area on which the lluid pressure acts may beinsuflicient to produce adequate total force for cxpanding the cuttersoutwardly against the formation to enlarge the diameter of the wellbore, or outwardly against a surrounding well casing to sever the same,Even with drill bits of larger size, suli'icient hydraulic pressure forexpanding its cutters outwardly may not be present because of inadequacyof the pumps, or in very deep holes because of the very substantialdiminution in fluid pressure caused by friction losses in pumping thetluid through comparatively long drilling strings,

An object of the invention is to provide an improved expansible rotarydrill bit, in which the hydraulic force available for expanding itscutters is assisted by supplementary means to assure proper and fullexpansion of the cutters. h

Another object of the invention is to provide an expansible rotary drillbit having cutters expandible :outwardly by a combination of hydraulicand spring forces, in which a spring device can be embodied in the bitcapable of exerting a comparatively great force.

A further object of the invention is to provide an expansible rotarydrill bit having cutters expandible outward ly by a combination ofhydraulic and spring forces, in which assembly of the spring iii the bitunder stress, as Well as its disassembly, can be accomplished rapidlyand with comparative ease.

An additional object of the invention is to provide improvedhydraulically operable, expansible rotary drill bit, in which thehydraulic force for expanding its cutters outwardly is assisted bysupplementary means that maintain the cutters expanded upon relieving ofthe hydraulic force.

Yet a further object of the invention is to provide an expansible rotarydrill bit having cutters expanded outwardly by a spring device, in whichthe cutters can still be shifted to their initial retracted position inthe event difficulty is encountered in returning the spring to itsinitial position within the bit.

This invention possesses many other advantages, and has other objectswhich may be made more clearly apparent from a consideration of a formin which it may be embodied. This form is shown in the drawingsaccompanying and forming part of the present specification. It will nowbe described in detail, for the purpose of illustrating the generalprinciples of the invention; but it is to be understood that suchdetailed description is not to be taken in a limiting sense, since thescope of the invention is best dened by the appended claims.

Referring to the drawings:

FIGURE 1 is a longitudinal section through an expansible rotary drillbit, with its cutters occupying a retracted position;

FIG. 2 is a view simliar to FlG. 1, disclosing the cutters in theiroutwardly expanded position.

United States Patent O ice A rotary expansible drill bit A isdisclosed'in the drawings, which is secured to the lower end of a stringof drill pipe B extending to the top of a well bore D, by means of whichthe drill bit is lowered through a string of well casing C to a desiredlocation where the cutters lll of the bit are to be expanded outwardly.The drill bit specifically disciosed has milling type of cutters lll tosever a casing section and mill it away along a desired length. Suchcutters are illustrated by way of example only, and it is to beunderstood that other type of cutters, whether they be drag or rollertypes, can be used depending upon the operation to be performed in thewell bore. The cutters illustrated can, if desired, be used forenlarging the diameter of the well bore D, as well as milling away asection of well casing C therewithin.

The upper portion of the rotary drill bit includes a manrel l1 having anupper pin l2 threadedly connected to the lower end of the string ofdrill pipe B. This mandrel includes an upper kelly or drill stem member13 slidably splined to the main body 1d of the bit. The exterior of thelower portion 15 of the kelly is non-circular in Shape, beingtelescopically received in a companion non-circular socket d6 formed inthe main bit body. Specifically, the kelly exterior and the socket maybe of hexagonal shape to enable the kelly 13 to be moved longitudinallywith respect to the body '14 while being capable of transmitting rotarymotion to the body.

The mandrel 11 has a limited range of longitudinal movement within thebody, its downward movement being determined by engagement of the lowerend 17 of the kelly with an inwardly directed body shoulder 18, and itsupward movement being limited by engagement of an external shoulder orpiston portion l@ of the kelly with a cylinder head Ztl secured to thebody. The upper end of the head has a flange Z1 engaging a body shoulder22, the flange being prevented from moving upwardly of the body by splitsnap retainer rings 23 fitting ina body groove Z4 and overlying theflange 2l,

'The body ld has a plurality of expansible parts mounted on it. Theseinclude cutter supporting members 25 pivotally mounted in body slots Z6on hinge pins 27 suitably secured to the body to prevent'their losstherefrom. Each cutter supporting member 25 depends from its hinge pin27 and carries a suitable cutter structure 1li, such as a drag ormilling cutter, at its lower end, which, as stated above, has thepurpose of severing and milling away a section of casing C, enlargingthe di-Y ameter of a well bore D, or both.

The cutter supporting members 25 and the cutter structures lllthemselves normally occupy a retracted position substantially entirelywithin the confines of the main body t4 of the bit. These cuttersupporting members and the cutter structure are expandible outwardly. Inthe use of the device illustrated in the drawings, their outwardexpansion can rst sever the casing C and then mill it away by operatingupon the upper-end E of the casing therebelow, or the cutter can actupon the upwardly facing shoulder F which they form in the enlarged wellbore D. To accomplish the expansion, each cutter supporting member 25hasvan inclined expander surface 30 on its inner portion below the hingepin 27 which tapers in a downward and inward direction. Each expandersurface terminates in a lock surface 31 formed on a lock portion 32 ofthe cutter supporting member. The outward expansion is accomplished byproducing relative longitudinal movement between the mandrel 11 and thebit body 14, which will produce relative longitudinal movement betweenthe cutter supporting members 25 and the tubular member 33 of themandrel. This tubular member includes a lower portion 34 slidable withina guide bushing 35 mounted in a bridge 36 secured to the bodyandextending across the body slots 25. This guide bushing 35 is disposedbelow the lockportions 32 of the cutter supporting members 25.

Located initially substantially above the guide bushing and below thehinge pins 27 land in .cutter member recesses 37 is a mandrel lock andexpander 38which has outer surfaces 39 adapted toV engage the expandersurfaces 30 and the lock surfaces 31.V The lock and expander 38 maybeformed integral with thev tubular member 33,'the upper end of thelatter being vpiloted within a socket 40 formed in the lower portion 15of the kelly. An enlarged boss 41 on the tubular member engages adownwardly facing shoulder 42' of the kelly, the tubular member 33 beingheld against this shoulder by a suitable split retainer or .lock ringV43 mounted in an internal groove 44 encompassing the kelly socket 40and 'engaging the lower end of the tubular member boss 41. Drilling mudor other uid can pass down through the central passagey 45 of the kellyVor drill -steml and Vinto the central passage 46g extending completelythrough the tubular member 33. Leakage of fluid around the exterior ofthe tubular member 33 is prevented'by a suitable side seal ring 47 inthe kelly which engages. the exterior of the boss 41. s v Y Y,

Assuming the body 14 of the tool to be elevated relasage 46 through thetubular member 33 ofthe mandrel 11 is of `a restricted diameter, ascompared to the pasat an adequate rate through the apparatus willbuildup a back pressure of'uid in the passage 45, which pressure Y willbe imposed on the fluid inV the cylinder'V space 56,

tively along the tubular mandrel 11, theinclinedexpander p surfaces ofthe cutter supporting members 25 will be shifted upwardly along the lockand expander portion 38 of the tubular member 33. During such upwardshiftward movementof the body 14 with respect to the tubularv mandrel 11can continue. untilV the cutter structures 10 have. been shiftedoutwardly to their fullest extent,

as determined by engagement 'of stop shoulders 50 onthe cuttersupporting vmembers with companion shouldersk 51 formed in the body onopposite sides of the body slots 26. When such engagement occurs, thelower end 17 of thekelly portion 13 of the tubular 'mandrel will engagethe body shoulder 18, and the lock and expander 38 on the tubular member33 will be disposedfbehind and-in engagementwith the lock portions 32 onthe cutter supporting members 25.

Relative longitudinal movement between the tubular mandrel 11 and thebody 14 ofthe tool is accomplished hydraulically. The enlarged pistonportion 19 on the drill stem 13 isreceived within acounterbore 52lformed on an intermediate portion 53 of the Vbody of the tool.` Thisintermediate portion actually constitutes a cylinder having aVcylindrical wall y54 Yextending from a 'lower shoulderrSS defining thebottom ofthe counterbore to the cylinder head 20. Y

A confined cylinder space56 isrformed between -the piston portion 19 ofthe kelly, the periphery of the kelly 13 above the piston, and thecylinderv 53. Asuitable packing or side seal ring 57 may vbe disposedinthe piston 19 which is adapted to slidably seal against thecylindrical wall 54 of theV cylinder. Fluid istherebypreventedifrom'passing in a downward direction between the piston 19 andthe cylinder 53. Fluid is4 also prevented from passing in Van upwardIdirection from -the annular cylinder space 56 by .an .inner side'sealring Y59 carried in the cylinder head 20 and slidably and sealinglyengaging the periphery of the kelly 13 `above the piston 19, and alsobyran outer side seal ring 58 disposed in the head'20 and sealinglyengaging the cylinder wall 54;

Fluid under pressure in the string of drillpipe B and in the tubularmandrel passage 45 can be `fed into the cylinder space 56 through one orrmore side ports 60 establishing, communication betweenthe central pasvsage through the kelly and the cylinder space. Such tiuid under pressureis developed in the specific tooldisclosed in the drawings by virtuelof.the faetthatthepasacting Vupon vthe cylinder head 20 to urge the body14 of the tool in an upward direction with respect to the tubularmandrel '11, to secure `'outwardexpansionrof the cutter supportingmembers 25 and,y cutter structures 10 Yto their fullestextent, as abovedescribed.

The upward movement of the body 1401:'v the .tool with respectto thetubular mandrel 11 is assisted, Vin the appa 1 ratus illustrated in thedrawings, by a spring 7i) .which adds its force to the hydraulic forceacting upwardly on the cylinder head 20'. vAs shown, the body 14includes a spring housing portion 71l extending upwardly from thecylinder 53, which isV spaced from the kelly 13 to provide an annularspring chamber 72 in which a helical compression spring 70` is disposed;The lower end of the spring bears againstfa thrust ring or flange73fwhich is prevented from moving downwardly by resting uponan'inherently contractable split retainer ring 74 disposed inaperipheral groove y75 in the. kelly and extending outwardly therefrom.The upper end of the spring 70 bears against'a spring seat 76 which isprevented from moving upwardly ofthe housing byvengaging a splitretainer ring f77 ,disposed in an'internal groove 78 in the housing. -Inorder to prevent entry of drilling mud, .or other well bore fluid andsubstances, into the spring housing 71, a guide 79 is releasablyinserted in the upper end of the housing, being retained in position bya split expansible spring-like ring 80 disposedin a groove 81 in theguide and received within an internal groove 82 in the upper end ofthehousing.

The` spring is constantly exerting a force on the housing '71 and body14 of the tool tending to elevate the latter along the mandrel 11' inorder to effect outward expansion of thecutter supporting members 25 andcutters 10. Such upward movement can occur since an adequate space Y 83is provided initiallybetween the cylinder head 20 and v stantial,thereby'allowing theuseof. aspring '70 having a largeinitjialvcompressive force. When disposed in its s initial position, the spring,for'example, may exert a force of 'about '1,500 pounds tending toelevate the body 14 along the mandrel 11 of the tool. This force willsupplement the force of thelhydraulic pressure acting upon the pressureeffective area of the .cylinder head 20 and tending to elevate the bodyof the tool along vthe mandrel, andgthereby effect outwardexpansionofthe cutters 10.

In the operation of the apparatus A, it is run in the well casing, thecutterl supporting members25 and cutters 10 occupying their initialretracted position, vdespite the tendency of the spring 70to expand thelatter. The outer sides of the cutter supporting members 25' willmerelyslide, along theV inner Wall of the casing C. When the desired locationin the well casing is reached at which the casing severing action orhole'enlarging operation Vis to commence,.the drill string B and therotaryv drill bit A Vare turnedat the. desired rate of speed and thepumps at the top of the vwell bore started to pump yfluid at a suicientrate through the drill pipe and into the mandrel passages 45, `46,building up a back pressure inthe kelly passage 45 and of the fluid inthe ports 60 and cylinderA space 56,1which lpressure acts upon thecylinder head 20 to urge the body 14, the cutter supporting members 25,

and the cutter structures l@ in an upward direction with respect to themandrel 11. Such upward movement is assisted by the force exerted by thespring 70, which spring force can, as in the example given above, bequite considerable. During upward movement of the body 14 relative tothe mandrel 11, the expander surfaces 3h are brought to bear against thelock and expander portion 3S of the mandrel, the cutter structures 1l)being urged in an outward direction against the wall of the well casingC, and gradually milling it away. During this operation, the apparatus Ais retained in substantially the same longitudinal position in the wellcasing. As the casing is cut away, the hydraulic force and the springforce acting upon the body 14 raises the latter and the cuttersupporting members Z5 and cutter structures 11D to a further extentuntil the cutters have completely severed the casing C. Continuedrotation of the drill pipe B and the pumping of fluid through the drillbit will cause the cutters 1h to cut away additional casing and dig intothe formation, the spring force and hydraulic force combining to expandthe cutters outwardly, until the cutters 1li have been expandedoutwardly to their fullest extent, as determined by engagement of thestop shoulders Si?, 51 with one another and the lower end 17 of thekelly portion of the mandrel with the body shoulder 18. With the partsin this position, the lock portion 32 of each cutter supporting member25 will bear against the lock and expander portion 38 of the tubularmember 33 to preclude inadvertent partial retraction of the cutterstructures 1li from their fully expanded position.

Downweight in a proper amount can now be imposed von the string of drillpipe B, which downweight is transmitted through the kelly 13 to the bodyshoulder 18, and from the body to the stop shoulders Si), 51 directly tothe cutter supporting members 25 and the cutter structures 10, urgingthe cutter structures against the upwardly facing severed end E of thewell casing and against the upwardly facing formation shoulder F. Theimposition of a proper downweight or drilling weight on the apparatusand its rotation at a proper speed will cause the cutters to act uponthe severed end E of the casing and the 'shoulder F to mill the casingaway, and also to drill away the formation shoulder. During such millingand drilling actions, drilling fluid is being pumped down through thedrill pipe in the apparatus, discharging from the latter and carryingthe casing cuttings and formation cuttings upwardly around the tool Aand the drill pipe B to the top of the hole.

After the desired length of casing C and hole D have been cut anddrilled away, the tool can be withdrawn from the well bore. Pumping offluid can cease and the drill pipe B and the drill bit A elevated in thewell bore D. The spring 70 will retain the body 14 upwardly along themandrel 11, so as to maintain the cutters in their outward expandedposition, until the cutter supporting arms engage the downwardly facingshoulder H provided by the upper severed end of the casing C, which willtend to prevent further upward movement of the tool. Accordingly, thetaking of a suicient upward strain on the drill pipe B and mandrel 11will cause the mandrel to move upwardly within the body 14 against theforce of the spring 7tl, compressing the latter and elevating the lockportion 38 of the mandrel above the lock and expander surfaces 31, ofthe tool, allowing the cutter supporting members 25 and cutters 10 toshift inwardly entirely within the contines of the body 14 and thecasing C. The tool, with the cutters in retracted position, can now beelevated through the casing to the top of the well bore, the cuttersupporting members 25 merely sliding along the inner wall of the wellcasing C.

In the absence of the spring 70, in the event the cutter members 25 wereelevated from the upwardly facing casing end E and the shoulder F, andthe pump pressure ceased, the body 14 of the tool would tend to dropdownwardly along the mandrel 11 and the cutters 10 could then shift to aretracted position. However, with the spring 7i) constantly exerting aforce holding the body 14 in its upward position with respect to themandrel 11, the relieving of the hydraulic pressure will not result inthe cutters 1d shifting to a retracted position. Instead, they willremain in their outwardly expanded position, such as disclosed in FIG.2.

In relatively small size tools, the effective area of the cylinder head2t), as compared to the hydraulic pressure available for action uponsuch head, may be insufficient to insure the exertion of suiiicientoutward force of the cutters 1lb against the casing C to sever thelatter upon rotation of the drill pipe B and the drill bit A, or toenlarge the diameter of the well bore D by bearing against the wall ofthe formation. Such ineffective huid pressure may not only be due to therelatively small annular area of the cylinder head, but to theunavailability of adequate pumps at the top of the well bore capable ofsupplying sufficient pressure. Even where large capacity and relativelyhigh pressure pumps are available, the use of the drill bit A at thelower end of a very long string of drill pipe B is associated with verysubstantial losses in iluid pressure due to the frictional resistance ofthe fluid owing through the pipe itself. In all of such instances wherehydraulic force may be inadequate, the presence of the comparativelystrong compression spring 71B acting between the mandrel 11 and body 14of the tool will insure tne supplementing of the hydraulic force, andthe presence of an adequate total force effecting full outward expansionof the cutters 19 for the purpose of fully severing the well casing C,or enlarging the well bore D to its fullest extent, or both, the body 14being elevated along the mandrel 11 to its fullest extent at which thelock portion E8 will hold the cutter supporting members 2S and cutters1t? in their outward expanded position.

The spring 7 il is readily assembled in the tool and disassembledtherefrom, being insertable in place through the upper end of thehousing portion '71 against the lower thrust ring or ange 73. Throughuse of a suitable spring compression tool, the spring seat 76 is placedon top of the spring and forced toward the thrust ring or flange 73 tocompress the later, whereupon the retaining ring 77 is inserted inplace, overlying the upper spring seat 76 and snapped Iinto its groove78. The annular guide '79 can then be mounted in place. The spring willshift the body 14 upwardly along the mandrel 11 to expand the cutters.To prevent such expansion and to start the tool in the casing C, aholding screw may he threaded in a hole 91 in 'the body, the screwoverlying the guide 79 and Ithereby preventing the spring 70 fromexpanding. Following inserting of the cut-ters 10 and supporting members25 in the casing C, the screw 9) may be removed and the tool A lowered`in the casing.`

When disassembly is desired, the annular guide 70 is easily removed inan upward direction from the upper end of the housing 71, land asuitable tool provided for shifting the spring seat 76 downwardly to aslight extent to relieve the annular ring 77 of the spring force,allowing the latter to be retracted from its groove 78 and removed fromthe housing, whereupon the spring force can be gradually released andthe spring 70 also removed from the housing.

Assurance is had that the cutters 1l) can 'be shifted to a retractedposition from their fully expanded position, despite the fact that itmight not be possible, due to foreign substances in the spring chamber72, for example, to recompress the spring 76 back to its initialposition after it has expanded and shifted `the body 14 upwardly alongthe mandrel 11 to its fullest extent, such as disclosed in FlG. 2. Toaccomplish this purpose, the lower side 92 of the groove 75 containingthe split retainer ring '74 against which the thrust ring 73 'bears canbe tapered in an upward and inward direction, engaging the lower end ofthe retainer ring. This ring 74 inherently tends to remain -in an inwardposi-tion and is vof such dimensions as to resist its outward expansionvfrom 'the groove '75. The exertion-of a suiiicient vupward force on themand-rel 11 of the tool will cause they ananas-a Y ing torque istransmitted'from said mandrel to said body; said body having a housingportion spaced laterally from said mandrehspring means in said housingportion actingupon said mandrel and housing portion for'elevat'- Y ingsaid body and cutter means with respect .to said mandrel to hold saidcutter means Vlaterally outward; and means releasably securing saidspring means Yto said mandrel and .being releasable in response to apredetermined portions 32 Vof lthe cutter supporting arms25,'allowing yeffect shifting of the retainer ring 74 from the groove 7 5.Y

If, for example, the maximum force exerted by thel spring is about 1,500pounds, the upwardiforce on the mandrel 11 required'to shift the ring 74Afrom itsY groove 75 may beV of the order of about 5,000 pounds,"thereby assuring that the retainer ring will normally remain wi-thin thegroove and serves as an abutment for the thrust ring or flange 73. whichretraction of the cutters cannot take place as a result of inability torecompress the spring'7ii, that the taking of a sucient upward pull onVthe mandrel 11 will expand the retainer ring 74 from its groove 75 andthereby `release the mandrel from the thrust ring 73, allowing themandrel to move upwardly within theV body V14 .to a position allowingfull retraction of the cutters 10,.

VI claim:

f1. In a rotary well drillingbit: a main body; cutter f means mounted onsaid body for expansion laterally outward of said body; a mandrellconnectible to aV drill string and slidably splined to said body,whereby drilling torque is transmitted from said mandrel to said body;

It is only under emergency ',cponditions,V in

mandrel; said mandrel having a iluid passage communito said mandrel tocause said expander means to expand said cutter means laterally outward.V Y

2. In a rotary well drilling bit: a main body; cutter meansmounted onsaid body for expansion laterally outward of said body; a mandrelconnectible to a drill vstring and slidably splined'to said body,whereby drilling torque is transmitted from said mandrel to said body;coengageable expander means on said mandrel and cutterVV means; saidbody havinga cylinder portion above said expander means slidably andsealingly engaging said mandrel; said mandrel having. a iiuid passagecommunieating with the drill string and cylinder portion to 'feed iuidunder pressure to said cylinder portion to elevate said body and cuttermeans with respect to said mandrel to cause said expander means toexpand said cutter means laterally outward; said body having |ahousiugport-ion above said cylinder portion in spaced relation to saidmandrel; and spring means in said housing portion acting upon saidmandrel and 'housing portion for elevating said body and cutter meanswith respect Ito said mann and lslidably splined to said body, wherebydrilling torque drel to Acause said expander means to expand said cutterf means laterally outward. n

3. In a rotaryV well drilling bit: a main body; cutter means mounted onsaid body `for expansion laterally out-'kV force. imposed thereon. bysaid mandrel to enable said mandrel to move upwardly with respect tosaid body and cutter means and allow said cutter lmeans to movelaterally inwardly to retracted position.

4. In a rotary well drilling bit: a main body; cutter means mounted onsaid body for expansion laterally outwart of .said body; means forVexpanding andholding said cutter means laterally outward, said expandingand holding means comprising. a mandrel connectible vto'vaidrill stringand slidably splined tofsaid body, whereby drilling torque istransmitted'fr'onr said mandrel to said body; said body having a housingportion spaced-laterally from said mandrel; a thrust-member surroundingYsaid mandrel; means releasable in response to a predetermined forceimposed thereon by said mandrel releasably securing said thrust memberto said mandrel; al seat member secured to said `housing portion; and ahelical Vcompressionfspning in Vsaid housing portion-bearing againstsaid members 'to elevate said body and cutter means with respect to saidmandrel to hold said cutter means laterally outward; release of said'releasable means enabling said mandrel to move upwardly with Vrespectto said'body and cutter means and allowsaid cutter means to moveinwardly to retracted position.

5. In :a rotary well drilling bit:V a malin body member; cutter meansmounted on. said body member for expansion laterally outward of saidbody member; means for expanding and holding said cutter means laterallyoutward, said rexpandingand holding means comprising a mandrel vmember`conne'ct-ible to la d-rill string vand slidably splined to said bodymember, whereby drilling'torqueis transmitted from said mandrel membertosaid body member; said body member having a housing portion spa-cedlaterally from said mandrel member; spring means in sa-id housingportion acting upon-said mandrel member and housing portion forelevating said :body member and cutter means with respect to saidmandrelmember to hold said cutter means laterally outward; and meansreleasably securing said spring means to one of `said members and beingreg lea-sable in Vresponse to a predetermined force imposed thereonby-said mandrel member to enable said mandrel member to move -upwardlywith respect to said body mem- Vber land cutter means andV allow said'cutter means to Imove laterally'inwardlyV to retracted position.

16. In a rotary well drilling bit: a main body; cutter means mounted onsaid body for expansion laterally outward of said body; afmandrelconnectible to a drill string is transmitted from said mandrel to saidbody; Coengageable `expander means on/said mandrel and cutter means;

saidV body having a ycylinder portion above said expander.

means slida'bly and sealingly engaging said mandrel; said mandrel havinga iiuid passage communicating with the drill string and cylinder portionto feed iluid under pressure toy said cylinderportion to elevate saidbody and cutter means with respect to Isaid mandrel to cause saidexpander means to expand said cutter means laterallyoutward; said bodyhaving a housing portion above said cylinder portion inspaced relationto said mandrel; a thrust member surrounding said mandrel; meansreleasable in response to a predetermined force imposed thereon by saidmandrelreleasably securing said thrust member .to said mandrel; a seatmembersecured to said housing portion; and a helical compression springin'said housing portion bearing against saidmembers to elevate said bodyand cuttermeansjwith respect to said mandrel'tocause said expander meansto expand said cuttermeans laterally outward.

7. In a rotary Well drilling bit: a main body; cutter means mounted on`said tbody `for expansion laterally out- Ward of said body; ya mandrelmember connectible to a drill string land slidably splined to said body,whereby drilling torque is transmitted from said mandrel member to saidbody; coengageable expander means on said mandrel member and cuttermeans; said body having a cylinder portion above said expander meansslidably and sealingly engaging said mandrel member; said mandrel memberhaving la Huid passage communicating with the drill string `andcylinder' portion to feed fluid under pressure to said cylinder portionto elevate said body and cutter means with respect to said mandrelmember to cause said expander means to expand said cutter meanslaterally outward; said Ibody having a housing member above saidcylinder portion in spaced relation to said mandrel member; spring meansin said housing member acting upon said mandrel member and housingmember for elevating said body and cutter means with respect to saidmandrel member to hold sa-id ycutter means laterally outward; and meansreleasably securing said spring means to one of said members and beingrele-asable in response t0 a predetermined force imposed thereon by saidmandrel member.

References Cited in the le of this patent UNITED STATES PATENTS2,122,332 Wurzinger June 28, 1938 2,500,125 Huber Mar. 7, 1950 2,710,172Kammerer June 7, 1955 2,719,700 Kammerer Oct. 4, 1955 2,755,071 KammererJuly 17, 1956 2,754,088 Kammerer July 10, 1956 2,799,477 Kammerer July16, 1957 2,922,627 Kammerer Jan. 26, 1960

1. IN A ROTARY WELL DRILLING BIT: A MAIN BODY; CUTTER MEANS MOUNTED ONSAID BODY FOR EXPANSION LATERALLY OUTWARD OF SAID BODY; A MANDRELCONNECTIBLE TO A DRILL STRING AND SLIDABLY SPLINED TO SAID BODY, WHEREBYDRILLING TORQUE IS TRANSMITTED FROM SAID MANDREL TO SAID BODY;COENGAGEABLE EXPANDER MEANS ON SAID MANDREL AND CUTTER MEANS; SAID BODYHAVING A CYLINDER PORTION ABOVE SAID EXPANDER MEANS SLIDABLY ANDSEALINGLY ENGAGING SAID MANDREL; SAID MANDREL HAVING A FLUID PASSAGECOMMUNICATING WITH THE DRILL STRING AND CYLINDER PORTION TO FEED FLUDUNDER PRESSURE TO SAID CYLINDER PORTION TO ELEVATE SAID BODY AND CUTTERMEANS WITH RESPECT TO SAID MANDREL